After the battle with Doakuder at Soukaizan (the "other" world where the rainbow has disappeared because of the devils), a demon world Devil came to Genseikai (human world) and stole Wataru's conscience. Because of that, Wataru's heart of justice and his memories of being Kyuuseishu (world savior) vanished. After Shibaraku and Himiko brought him back to Shinbukai (the "other" world, where Soukaizan is located), Wataru regained his memories, however his conscience was still missing. (myanimelist.net)